One of the nicest additions in Office for the Tablet PC is the ability to ink Powerpoint presentations. I believe that if it could be recorded and synchronized with the audio stream and the whiteboard content, watching the presentation's online would nearly be as good as watching it live.
In the last two years I have watched many recorded talks which had video+audio stream with synchronized slides. But in my opinion the video (even though it was filmed and edited professionally) wasn't that useful. It mostly added pain to the playback (longer buffering times), but it didn't help understanding the talk.
That is because that cameras don't capture whiteboards and also when the speaker points at something on his slide, he is not pointing at your copy of the slide, but instead the hard-to-read filmed one. Instead, if the speaker was using some kind of digital cursor (Tablet pen or other) to point and annotate his slide and a digital whiteboard, the useful "live" content would be better recorded.
The only cases where the video was useful was when demos were shown. But again, this would better handled by recording the computer's feed than filming the screen ;-)
Also, in many cases, the Q&As are difficult to hear because you can't hear the question (the public doesn't have a mike). Sometimes the speaker repeats the questions, but that is actually pretty rare and isn't perfect (it slows down the presentation).
Loren talks about computers collaborating to record the audio in the conference room, like a distributed microphone array. It is probably a difficult problem: each microphone has its own directional characteristics, there is ooclusion by other attendees, reverberation everywhere and usually quite some noise. But it would definitely be quite powerful.
Update: Microsoft, in collaboration with some universities, has published some recorded talks, under the Multi-University/Research Laboratory (MURL) project. Although I find it awesome to have these lectures available, the video-only presentation doesn't benefit these recordings. Some lectures have synchronized slides, but some are filmed instead, which makes them really hard to read.